To understand the molecular basis of signal transduction through TRAF2, we propose to collect MAD data to determine the crystal structure of the C-terminal portion of TRAF2. TRAF proteins associate with and transduce signals from TNF receptor superfamily members to regulate various inflammatory and immune responses. To date, no detailed structural information has been obtained for this class of proteins. We expect our crystal structure to reveal how TRAFs oligomerize, and how oligomerization plays a role in receptor specificity. We have successfully grown crystals of the C-terminal TRAF domain of TRAF2. The crystals diffract to 3.0 E, and we expect soon to obtain a heavy atom derivative.